The
observation of the region of the sky in which it is believed Planet
X should now be, based on perturbations observed in the motions
of Uranus and Neptune, was determined, and there was no reason
to update that determination. A limited area of that region was
photographed, and that will be continued. A given area is photographed
with the twin 20 cm astrograph in New Zealand on two successive
nights near the time that area is in opposition, and these plates
are blinked in Washington to identify anything that has moved.
The predicted region is in the south, which requires observations
from a southern station, and it is in opposition in the April
to June period, which means observations have not yet started
for the year. Blinking will be done as soon as the plates are
received in Washington.

Observed
positions of Uranus and Neptune along with residuals in right
ascension and declination are used to constrain the location of
a postulated tenth planet. The residuals are converted into residuals
in ecliptic longitude and latitude. The results are then combined
into seasonal normal points, producing average geocentric residuals
spaced slightly more than a year apart that are assumed to represent
the equivalent heliocentric average residuals for the observed
oppositions. Such a planet is found to most likely reside in the
region of Scorpius, with considerably less likelihood that it
is in Taurus.

It
is proposed that the systematic residuals in the positions of
Uranus and Neptune may be due to an unknown planet: Planet X.
Using the weighted-least-squares method, the orbit and mass of
Planet X were computed from the residuals of Uranus. It is concluded
that, if it exists, Planet X will be the tenth planet. However,
it may not be the tenth from the sun since the computed semimajor
axis is a little less than Pluto's. Planet X's perihelion, like
Pluto's, is inside the orbit of Neptune.

Mass
and orbit estimation of Planet X via a family of cometsNeuhaeuser, R.; Feitzinger,
J. V.

Characteristics
of Planet X are developed by examining the aphelion distances
and orbital parameters of comets that are assumed to beinfluenced
by the unobserved planet. Planet X's semimajor axis and orbital
eccentricity are found by, respectively, averaging the apheliondistances
and studying the orbits of certain transplutonic comets. The orbital
inclination is also estimated based on the assumed role of Planet
Xin directing quasi-periodic comet showers toward the inner solar
system. The mass of the planet is calculated by extrapolating
the densitydistribution of the primordial solar nebula. A list
of assumptions including the cause of planetary perturbations
is used to describe the actual location of Planet X including
declination and ecliptic longitude as well as the apparent brightness.

Theoretical
models of solar-system dynamics which predict the existence of
a 10th planet (planet X) are surveyed and compared with recent
observations. The history of the discoveries of Neptune and Pluto
on the basis of discrepancies in the orbit of Uranus is recalled
in detail, and the persistence of such discrepancies in 9-planet
computations is considered. Particular attention is given to ongoing
efforts to compute the current position of planet X, and to ground-based
and space-based (IRAS and Pioneer) searches. Diagrams and graphs
are provided.